The Development of Analytical Procedures for Analysis of Trace Metals in Pharmaceutical Formulations and the Speciation of Arsenic in Antacids

Thiab, SHH
(2018)
The Development of Analytical Procedures for Analysis of Trace Metals in Pharmaceutical Formulations and the Speciation of Arsenic in Antacids.
Doctoral thesis, Liverpool John Moores University.

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Abstract

The reliability of data obtained from the existing United States Pharmacopeia (USP) method, USP <231> for elemental impurities (EI) have been questioned in the literature. New regulations regarding EI in pharmaceutical products were recently implemented on the 1st January 2018. The new regulations are USP <232>/<233> and the International Council for Harmonisation equivalent guidelines (ICH Q3D). The new regulations include the use of instrumentation such as inductively coupled plasma optical emission spectroscopy (ICP-OES) and inductively coupled plasma mass spectrometry (ICP-MS). The aim of this work was to develop, optimise and validate analytical methods for the determination of Class 1 and Class 2A elements, arsenic (As), cadmium (Cd), mercury (Hg),lead (Pb), cobalt (Co), nickel (Ni) and vanadium (V) simultaneously in pharmaceutical products in compliance with the new guidelines. The developed ICP-OES and ICP-MS methods were validated using the only available solid standard reference material (SRM) NIST 3280 Multivitamin/Multielement tablets. It was found that relying solely on spiked addition technique as suggested by USP<233> is inefficient as it may not reflect clearly the method’s accuracy particularly when the sample preparation involves the use of microwave (MW)-assisted acid digestion step, which is very common for pharmaceutical samples. Sample preparation was performed using a developed MW-assisted acid digestion method with reverse aqua regia. It was found that reaching a temperature of 210°C for sample’s digestion is necessary to get EI recoveries of greater than 95% and pre-digestion grinding was found to be beneficial to minimise variation in data and get relative standard deviation (RSD)of less than 5%. The validation results showed good linearity (R2>0.995) over a wide range with low limits of detection (LoDs) and limits of quantification (LoQs). The calculated LoQs in ng/mL are As (5.86, 1.149), Cd (0.87, 0.037), Hg (2.23, 1.701) Pd (4.73, 0.041), Co (1.58, 0.299), Ni (1.74, 0.159) and V (7.64, 0.485) for ICP-OES and ICP-MS incorporated with collision reaction cell (CCT) respectively. Twenty-four commercially available pharmaceutical products including analgesic tablets, cough remedies, flu powders and antacids were analysed. Four products contained Cd in concentrations exceeding the permitted daily exposure limit (PDE) of 5µg/day when the maximum dose is taken, and nine products exceeded the 5µg/day PDE of Pb. This is especially concerning for the paediatric products because children are more susceptible to EI adverse effects as for example, they can absorb up to 40-70% of ingested Pb. The antacids were found to contain As and although the levels quantified were below the PDE (15µg/day), a speciation method using an ion-pair reversed phase high performance liquid chromatography (HPLC)-ICP-MS was optimised and validated according to ICH Q2B guidelines as no information regarding what species are present in such products is available in the literature. Four arsenic species were selected, arsenite (AsIII), arsenate (AsV), monomethyl arsonate (MMA) and dimethyl arsenate (DMA). Calibrations with R2>0.995 for all four species in the range of 1 to 50 ng/L and % recoveries>95% with RSD<5% were obtained. Arsenic was extracted from the samples using MW assissted extraction with 0.3M phosphoric acid at 55°C for 10 miutes, 75°C for 10 minutes and 95°C for 1 hour. The species were stable after being exposed to the extraction procedure (spiked recoveries >95%). This method was able to extract 95% or more of arsenic for all products. The ion-pair reversed phase chromatography was performed using a mobile phase: 10mmol/L tetrabutylammonium, 20mmol/L potassium dihydrogen orthophosphate and 2% methanol at pH 6 with a C18 column. The speciation analysis results for all the antacids showed that approximately 50% of the extracted As was present as the most toxic AsIII form. The work demonstrates some of the potential issues with the new regulations and the availability of suitable solid SRM and seeks to provide workable solutions for the analysis.